The songs had to get onto your iPhone 11 Pro in some way... did you purchase them from the iTunes store? If so, you can download them again from the iTunes Store.
Learn how to redownload music that you purchased from the iTunes Store on your iPhone or iPad.
support.apple.com
Did you purchase them using a different music store? If so, you can probably redownload them from that store's app.
Otherwise, you would have had to sync the music files on a computer to your iPhone 11 Pro at some point. If you don't have a computer anymore and did not back up the music files.... well, you'll need a computer and you will need to sync the music files from the iPhone 11 Pro to the computer. I'm partial to iMazing for this job.
iMazing lets you transfer music, files, messages, apps and more from any iPhone, iPad, or iPod to a computer, Mac or PC. Manage and backup your iOS device simply without iTunes. (was DiskAid)
imazing.com